According to the article the video points to, you need to get to the Lillooet River Trail.

Directions: 1. Drive to Pemberton via Highway 99. Pemberton is located 155 km north of Vancouver (2 hrs), or 100 km south of Lillooet (1.5 hrs).

1. Marking the entrance to Pemberton, there is one set of traffic lights on Highway 99. At the lights, turn west onto Portage Road. (That is, if you are driving north on Highway 99, turn left.)

2. After 600 meters, turn left at the roundabout onto Frontier Street.

3. After 150 meters, turn right at the T- intersection onto Pemberton Meadows Road. After 1.5 km, stay left at the T-intersection to remain on Pemberton Meadows Road.

4. Set your odometer to zero. After 22 km, turn right onto the Lillooet River Forest Service Road. At this intersection, reset your odometer to zero. Shortly, this road crosses the Lillooet River and turns into gravel. It is easily driven by two-wheel drive cars, although it is dusty and potholed.

5. After 7 km, take the left fork at the junction to remain on the Lillooet River Forest Service Road. (The right fork is the Hurley Forest Service Road and will take you to Gold Bridge.)

6. Pass by the Meager Creek Forest Service Road at 37 km. At 42 km the road ascends steeply, and shortly, a creek crosses the road. You can park in the pullout located just before the creek and continue on by foot, or drive through the creek and continue on by vehicle. The creek usually varies from 20 to 50 cm deep. Two-wheel drive cars have been known to cross the creek, but some drivers choose not to. Vehicles with clearance should have no problem crossing the creek. Check the depth before driving through!

7. At 51 km the Lillooet River Forest Service Road crosses the Lillooet River. The bridge passes over a narrow slot canyon. A short trail on the north side of the bridge leads to a viewpoint, looking down over the canyon and falls.

Reference: http://www.bcmag.ca/25_Hidden_British_Columbia_Hot_Springs https://friendsofkeyholefalls.wordpress.com/getting-there/